JP2008112724A - Catalyst for positive electrode and lithium air secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for a positive electrode for a lithium air secondary battery and a lithium air secondary battery enabling charging at low voltage when charging and enabling discharging at high voltage when discharging. <P>SOLUTION: The catalyst for the positive electrode used in the positive electrode 2 of the lithium air secondary battery 1 is provided with nonaqueous electrolyte as electrolyte solution as well as a negative electrode 3 composed of metal Li. This catalyst for the positive electrode contains metal oxide with a function to absorb and discharge oxygen. The lithium air secondary battery 1 also contains the catalyst for the positive electrode in the positive electrode 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive electrode catalyst for a lithium air secondary battery having a nonaqueous electrolytic solution as an electrolytic solution and having a negative electrode made of metal Li, and a lithium air secondary battery using the positive electrode catalyst.

An air battery is a battery having a positive electrode using oxygen in the air as an active material. The air battery can charge and discharge the battery by oxidizing and reducing oxygen at the positive electrode.
As a specific air battery, a battery having a negative electrode made of metal and containing, for example, a porous carbon material capable of oxidizing and reducing oxygen on the positive electrode has been proposed (see Patent Document 1). In such an air battery, it has been proposed to use a perovskite type compound as a catalyst for the positive electrode of an air battery containing an aqueous electrolyte solution in order to promote oxidation and reduction of oxygen (see Patent Document 1). It has also been proposed to use La _1-x Ca _x CoO ₃ (0.05 ≦ x ≦ 0.9) as a catalyst (see Patent Document 2).

  However, these conventional air batteries are batteries using an aqueous electrolyte solution. In an air secondary battery using such an aqueous electrolyte, it is very difficult to return the metal hydroxide generated after discharge to metal again during charging. In particular, when an alkali such as lithium or an alkaline earth metal is used for the negative electrode, these may react with the aqueous electrolyte and the negative electrode may be deactivated. Therefore, the air battery has actually only been used as a primary battery using a metal such as Zn or Al for the negative electrode.

On the other hand, an air secondary battery using a non-aqueous solvent has also been proposed. Specifically, a lithium-air secondary battery that contains cobalt as a catalyst in the positive electrode and metal lithium in the negative electrode has been proposed (see Non-Patent Document 1).
Further, as an air secondary battery, for example, an air lithium secondary battery that includes lithium peroxide and lithium oxide in a positive electrode and has a solid electrolyte layer as an electrolyte has been proposed (see Patent Document 3).

However, many non-aqueous solvents such as organic solvents may be decomposed when a potential of 4.3 to 4.6 V or more is applied. Therefore, in order to obtain stable charge characteristics, a reduction in overvoltage during charging is required. At the same time, it is required to increase the discharge voltage by reducing the overvoltage. In the conventional lithium-air secondary battery, the decrease in overvoltage during charging is insufficient, and the voltage during discharging is also insufficient.
In addition, in the conventional air secondary battery using a solid electrolyte layer, the problem of a decrease in overvoltage is unavoidable. Therefore, the discharge voltage becomes insufficient, and there is a possibility that the voltage rapidly increases during charging.

JP-A-2005-190833 JP-A-2-257777 Japanese Patent Laid-Open No. 2005-166585 KM Abraham, Z. Jiang, "ELECTROCHEMICAL SCIENCE AND TECHNOLOGY", Journal of the Electrochemical Society (USA), published in January 1996, Volume 143 (Vol. 143), No. 1 (No. 1) p. 1-5

  The present invention has been made in view of such a conventional problem, and enables positive charge for a lithium-air secondary battery that can be charged at a low voltage during charging and can be discharged at a high voltage during discharge. The present invention intends to provide a catalyst for use and a lithium-air secondary battery.

1st invention is a catalyst for positive electrodes used for the positive electrode of the lithium air secondary battery which has a nonaqueous electrolyte solution as electrolyte solution, and has a negative electrode which consists of metal Li,
The positive electrode catalyst is a positive electrode catalyst characterized in that it contains a metal oxide having an oxygen absorption / release capacity.

The second invention is a positive electrode catalyst used for a positive electrode of a lithium-air secondary battery having a nonaqueous electrolytic solution as an electrolytic solution and having a negative electrode made of metal Li,
The positive electrode catalyst contains a metal oxide having an oxygen absorption / release capability,
The metal oxide is a positive electrode catalyst characterized by containing at least MnO ₂ (Claim 6).

A third invention is a positive electrode catalyst used for a positive electrode of a lithium air secondary battery having a nonaqueous electrolytic solution as an electrolytic solution and a negative electrode made of metal Li,
The positive electrode catalyst contains a metal oxide having an oxygen absorption / release capability,
The metal oxide contains a perovskite complex oxide represented by ABO ₃ , and the perovskite complex oxide contains at least two selected from La, Sr, and Ca as an A site element, A positive electrode catalyst comprising at least one selected from Mn, Fe, Cr, and Co as a B-site element (Claim 7).

The positive electrode catalyst of the first invention contains at least CeO ₂ as a metal oxide having oxygen absorption / release capability.
Further, the positive electrode catalyst of the second invention contains at least MnO ₂ as a metal oxide having oxygen absorption / release capability.
The positive electrode catalyst of the third invention contains a perovskite complex oxide represented by ABO ₃ as a metal oxide having oxygen absorption / release ability, and the perovskite complex oxide comprises an A site element. At least two selected from La, Sr, and Ca, and at least one selected from Mn, Fe, Cr, and Co as the B site element.
Therefore, when the positive electrode active material of the first to third inventions is used for the positive electrode of the lithium air secondary battery, the positive electrode catalyst can promote oxygen redox. Therefore, the overvoltage of the lithium air secondary battery can be reduced. As a result, the lithium air secondary battery can be discharged at a higher voltage and charged at a lower voltage.

  That is, the lithium-air secondary battery is a battery using Li metal for the negative electrode and oxygen in the air for the positive electrode as the active material. At the time of discharge, oxygen is reduced at the positive electrode, and the reduced oxygen reacts with Li ions from the negative electrode to generate Li oxide. At this time, since the amount corresponding to the overvoltage due to the energy spent for the reduction of oxygen is subtracted from the theoretical discharge voltage, the actual discharge voltage is lower than the theoretical discharge voltage. Since the positive electrode catalyst of the present invention can reduce the overvoltage, the discharge voltage can be improved as described above.

  On the other hand, during charging, the Li oxide is reduced to generate oxygen. At this time, the positive electrode catalyst can promote the generation of oxygen. Therefore, the overvoltage can be reduced, and charging at a low voltage is possible. The positive electrode catalyst enables charging at a voltage sufficiently lower than the potential at which the nonaqueous electrolyte decomposes (for example, about 4.5 V). Therefore, a lithium air secondary battery having a non-aqueous electrolyte can be realized by using the positive electrode catalyst.

The reason why the positive electrode catalyst promotes charging and discharging as described above will be described.
That is, in a lithium air secondary battery, oxygen reduction occurs during discharging, and oxygen release occurs during charging. Therefore, in the battery, it is required that oxygen is supplied during discharging and that oxygen is recovered during charging. The positive electrode catalyst has the ability to absorb and release oxygen. Therefore, supply of oxygen at the time of discharging and recovery of oxygen at the time of charging can be promoted.
Therefore, in the lithium air secondary battery, the positive electrode catalyst enables charging at a low voltage during charging, and enables discharging at a high voltage during discharging.

The fourth invention is a lithium air secondary battery having a non-aqueous electrolyte as an electrolyte and a negative electrode made of metal Li.
The lithium air secondary battery is a lithium air secondary battery characterized in that the positive electrode catalyst according to any one of claims 1 to 9 is contained in a positive electrode (claim 10).

The most notable point in the lithium air secondary battery of the fourth invention is that the positive electrode catalyst of the first to third inventions is contained in the positive electrode.
Therefore, in the lithium air secondary battery, the positive electrode catalyst can promote the charge / discharge reaction. Therefore, the lithium air secondary battery can be charged at a low voltage during charging, and can be discharged at a high voltage during discharging.

Next, a preferred embodiment of the present invention will be described.
In the first to third inventions, the positive electrode catalyst is a perovskite complex oxide represented by at least CeO ₂ , MnO ₂ , or ABO ₃ as a metal oxide having oxygen absorbing / releasing ability (however, A site element: at least two selected from La, Sr and Ca, and B site element: at least one selected from Mn, Fe, Cr and Co).
The oxides of various metal elements described above can absorb and release oxygen by changing the valence of the metal element. For example, in the case of an oxide of a tetravalent metal element M, the absorption / release reaction of 2MO ₂ → M ₂ O ₃ + 1 / 2O ₂ and M ₂ O ₃ + 1 / 2O ₂ → 2MO ₂ proceeds, and the atmosphere at the catalyst active point It is considered that the reaction is promoted by changing the oxide according to the above.

In the first invention, the positive electrode catalyst preferably contains a solid solution of CeO ₂ (Claim 2).
In this case, the ability to absorb and release oxygen of the positive electrode catalyst can be further improved.
As the solid solution, a combination of CeO ₂ and an oxide such as Zr, Y, or Nd can be employed.

Preferably, the positive electrode catalyst preferably contains a solid solution of CeO ₂ and ZrO ₂ (Claim 3).
In this case, the ability to absorb and release oxygen of the positive electrode catalyst can be further improved.

Further, the catalyst for the positive electrode preferably contains a composite of CeO ₂ and Al ₂ O ₃ (claim 4).
Also in this case, the ability of the positive electrode catalyst to absorb and release oxygen can be further improved.

The composite material may be obtained by adding an alkali to an aqueous solution obtained by dissolving a cerium salt and an aluminum salt in water to form a precipitate containing cerium hydroxide and aluminum hydroxide, and firing the precipitate. Preferred (claim 5).
In this case, the ability to absorb and release oxygen of the positive electrode catalyst can be further improved.

  As said cerium salt and said aluminum salt, nitrate, sulfate, hydrochloride, acetate, etc. of cerium and aluminum can be used, respectively. As the alkali, ammonia, ammonium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, or the like can be used.

Moreover, it is preferable to age | cure the said precipitate at the temperature of 100 to 200 degreeC before baking of the said precipitate. In this case, the production of cerium hydroxide and aluminum hydroxide can be promoted, and the content of cerium hydroxide and aluminum hydroxide in the precipitate can be increased.
When the aging temperature is less than 100 ° C., the production of cerium hydroxide and aluminum hydroxide may not be promoted sufficiently. On the other hand, when it exceeds 200 ° C., the water vapor pressure becomes high, and a device that can withstand high pressure is required, which may increase the production cost. More preferably, it is 100 ° C to 150 ° C.

Moreover, it is preferable to perform baking of the said precipitate at the temperature of 500 to 900 degreeC.
When the temperature is lower than 500 ° C., the composite material of CeO ₂ and Al ₂ O ₃ is in an amorphous state, which may deteriorate the stability of the catalyst performance. On the other hand, when it exceeds 900 ° C., the surface area of the composite material becomes small, and the effect of improving the ability to absorb and release oxygen may be reduced.
Moreover, although baking of the said precipitate can be performed by dividing into two or more steps temperature, the final baking temperature can be made into the above-mentioned 500 degreeC-900 degreeC.

In the third invention, the catalyst for a positive electrode contains a perovskite complex oxide represented by ABO ₃ as the metal oxide, and the perovskite complex oxide contains La as an A site element, It contains at least two selected from Sr and Ca, and contains at least one selected from Mn, Fe, Cr, and Co as the B site element.
Specifically, for example, a perovskite type complex oxide containing La and Ca in the A site element and Co in the B site element can be used.

It is preferable that a noble metal is supported on the metal oxide.
In this case, the reduction and generation of oxygen molecules can be greatly promoted.
Specifically, as the noble metal, for example, one or more metals selected from Pt, Rh, Pd, Ag, Ru and the like can be used.

The positive electrode catalyst is preferably used for the lithium-air secondary battery that is charged at an average voltage of 3.5 V to 4.3 V (Claim 9).
In this case, the characteristics of the positive electrode catalyst that can be charged at a relatively low voltage at room temperature can be fully utilized.

Next, the lithium air secondary battery contains a non-aqueous electrolyte as an electrolyte.
The non-aqueous electrolyte can be prepared by, for example, dissolving an electrolyte in an organic solvent.
As the electrolyte, for example, a lithium salt can be used. In this case, the lithium salt is dissociated by dissolving in an organic solvent and becomes lithium ions and is present in the electrolytic solution. Examples of the lithium salt that can be used include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _{2 and the} like. These lithium salts may be used alone or in combination of two or more thereof.

  As the organic solvent for dissolving the lithium salt, an aprotic organic solvent can be used. As such an organic solvent, for example, a mixed solvent composed of one or more selected from cyclic carbonate, chain carbonate, cyclic ester, cyclic ether, chain ether, and the like can be used.

  Here, examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the upper cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. As the organic solvent, any one of these can be used alone, or two or more kinds can be mixed and used.

The positive electrode of the lithium-air battery is preferably formed by pressure-bonding a positive electrode material containing the positive electrode catalyst, a carbon material, and an organic binder to a current collector.
In this case, the positive electrode for the lithium-air battery can be easily produced.

As the carbon material, it is preferable to use a porous carbon material having a large surface area.
In this case, the contact area with oxygen is increased, and the charge / discharge capacity of the lithium air electrode can be improved. Specifically, for example, activated carbon, graphite, carbon black, coke, and carbon fiber can be used.

Moreover, as said organic binder, polytetrafluoroethylene, a polyvinylidene fluoride, carbon fiber etc. can be used, for example.
As the current collector, for example, a Ni mesh, an Au mesh, a stainless mesh, or the like can be used.

The positive electrode catalyst preferably occupies 0.01 to 50% by mass in the total amount of the positive electrode catalyst, the carbon material, and the organic binder in the positive electrode (claim 12).
When the proportion of the positive electrode catalyst is less than 0.01% by mass, the effect of the present invention by the catalyst may be insufficient. On the other hand, when it exceeds 50 mass%, the electroconductivity of a positive electrode falls and there exists a possibility that the electric current which can be taken out from a battery becomes inadequate. More preferably, 2-30 mass% is good.

  As the negative electrode, metallic lithium can be used. As said negative electrode, metallic lithium can be shape | molded and used for desired shapes, such as plate shape, for example.

As the detailed configuration of the lithium air secondary battery, various configurations of air batteries known at the present stage can be adopted.
Specifically, the lithium-air secondary battery includes a separator that separates the positive electrode and the negative electrode, and the non-aqueous electrolyte, and the positive electrode has air on the side opposite to the separator. It is preferable to have a contact part with (claim 13).
In this case, a lithium air secondary battery exhibiting the effects of the present invention can be easily configured.
The metal oxide contained in the positive electrode catalyst can absorb and release oxygen by an oxidation-reduction reaction at the contact portion with air (claim 14).

As the separator, a porous separator made of polyethylene, polypropylene, or the like can be used.
Further, the non-aqueous electrolyte can be impregnated in the separator. In this case, the separator impregnated with the non-aqueous electrolyte can be sandwiched between the positive electrode and the negative electrode.

An oxygen permeable membrane can be disposed on the contact portion side on the positive electrode.
In this case, it is possible to prevent moisture from entering while supplying oxygen to the positive electrode of the lithium-air secondary battery.
As the oxygen permeable membrane, a water-repellent porous membrane that allows oxygen in the air to permeate and prevents moisture from entering can be used. Specifically, for example, a porous film made of polyester, polyphenylene sulfide, or the like can be used.

(Example 1)
Next, an embodiment of the present invention will be described with reference to FIGS. In this example, a positive electrode catalyst for a lithium air secondary battery is produced, and a lithium air secondary battery is produced using the positive electrode catalyst.

As shown in FIGS. 2 and 3, the positive electrode catalyst 23 of this example has a non-aqueous electrolyte as an electrolyte and a catalyst used for the positive electrode 2 of the lithium air secondary battery 1 having the negative electrode 3 made of metal Li. It is. The positive electrode catalyst 23 contains a metal oxide having the ability to absorb and release oxygen. The positive electrode catalyst 23 of this example contains a CeO ₂ —ZrO ₂ solid solution as a metal oxide, and a noble metal is supported on the solid solution.

  As shown in FIGS. 1 to 3, the lithium-air secondary battery 1 of the present example includes a nonaqueous electrolytic solution as an electrolytic solution, a positive electrode 2 that oxidizes and reduces oxygen, and a negative electrode 3 made of metal Li. As shown in FIG. 3, the positive electrode 2 is formed by pressure-bonding a positive electrode material 25 containing a positive electrode catalyst 23, a carbon material 22, and an organic binder (not shown) to a current collector 21.

As shown in FIG. 2, in the lithium air secondary battery 1, the positive electrode 2, the negative electrode 3, and the electrolytic solution are disposed in the battery case 6. A separator 4 is disposed between the positive electrode 2 and the negative electrode 3, and the non-aqueous electrolyte is impregnated in the porous separator 4. Further, the positive electrode 2 has a contact portion 27 with air on the side opposite to the separator 4. An oxygen permeable film 5 is disposed on the surface of the positive electrode 2 on the contact portion 27 side.
As shown in FIGS. 1 and 2, the battery case 6 includes a body portion 61, a lid portion 62, and an insulating portion 63. The lid portion 62 is provided with a through hole 625 for introducing air into the battery. ing. Oxygen enters the lithium air secondary battery 1 from the through hole 625, and this oxygen passes through the oxygen permeable membrane 5 and is supplied to the positive electrode 2. Further, the main body portion 61 and the lid portion 62 of the battery case 6 are joined by caulking, welding, or the like via an insulating portion 63 made of an insulating material.

Next, the manufacturing method of the lithium air secondary battery of this example will be described. First, a positive electrode catalyst was prepared as follows.
That is, first, cerium nitrate and zirconyl nitrate were mixed in water to prepare a mixed aqueous solution. At this time, cerium nitrate and zirconyl nitrate were mixed so that the mixing ratio of CeO ₂ and ZrO ₂ in the target CeO ₂ —ZrO ₂ solid solution was 5: 1. Next, while stirring the mixed aqueous solution in a beaker, aqueous ammonia was dropped into the mixed aqueous solution to neutralize it, thereby generating a precipitate. The resulting precipitate was heated in the atmosphere at a temperature of 400 ° C. for 5 hours to evaporate and decompose the coexisting ammonium nitrate. Further, CeO ₂ —ZrO ₂ solid solution powder was obtained by firing at 600 ° C. for 5 hours in the air.

Next, dinitrodiammine platinum nitric acid is dissolved in 150 ml of water so that the amount of platinum contained therein is 5 g, and an aqueous solution is prepared. To this aqueous solution, 90 g of CeO ₂ —ZrO ₂ solid solution powder is added. After mixing, the mixture was heated at a temperature of 500 ° C. for 3 hours to obtain a positive electrode catalyst comprising a CeO ₂ —ZrO ₂ solid solution carrying platinum. This is designated as Sample E1.

Next, a lithium air secondary battery 1 as shown in FIGS. 1 and 2 is manufactured using the sample E1.
Specifically, first, the positive electrode 2 was produced as follows.
That is, first, 14.6 parts by weight of the positive electrode catalyst (sample E1) 23 and 83 parts by weight of activated carbon 22 were mixed in ethanol to prepare a mixed solution. A thin film positive electrode material 25 was obtained by mixing 2.4 parts by weight of polytetrafluoroethylene with this mixed solution. Next, a positive electrode material 25 in an amount containing 5 mg of activated carbon 22 was pressed against a metal mesh (current collector) 21 made of Ni and vacuum-dried to obtain a plate-like positive electrode 2 (see FIG. 3).

Next, as shown in FIG. 2, a plate-like Li metal was prepared as the negative electrode 3. Further, the nonaqueous electrolytic solution was prepared by dissolving 1M LiPF ₆ as an electrolyte in a solvent in which 30 parts by weight of ethylene carbonate (EC) and 70 parts by weight of diethyl carbonate (DEC) were mixed. As the separator 4, a porous polyethylene sheet was prepared.

  Next, as shown in FIG. 2, the positive electrode 2 and the negative electrode 3 produced as described above are arranged in the main body 61 of the battery case 6 so as to be separated by a separator 4 previously impregnated with a nonaqueous electrolytic solution. . At this time, as shown in FIGS. 2 and 3, the positive electrode 2 was arranged in the battery case 6 so that the surface on which the positive electrode material 25 was applied was on the separator 4 side. Subsequently, the oxygen permeable membrane 5 was disposed on the contact portion 27 with oxygen which is the surface on the opposite side of the separator 4 on the positive electrode 2. Next, the lid portion 62 having a plurality of through holes 625 formed therein was disposed in the opening portion of the main body portion 61 of the battery case 6, and the lid portion 62 and the main body portion 61 were joined. Thus, the lithium air secondary battery 1 as shown in FIG.1 and FIG.2 was produced. This is referred to as a battery E1. Although not clearly shown in this example, the positive electrode 2 and the negative electrode 3 are provided with terminal portions (not shown) that are electrically connected to the outside of the battery case 6, and these terminal portions are connected to the battery. Charging and discharging can be performed.

In this example, instead of the positive electrode catalyst (sample E1) made of CeO ₂ —ZrO ₂ solid solution carrying platinum, a positive electrode catalyst (sample E2) made of La _0.6 Ca _0.4 CoO ₃ was used for lithium. An air secondary battery (battery E2) was produced.
Specifically, first, calcium nitrate, lanthanum nitrate, and cobalt nitrate were mixed in water at a molar ratio of La: Ca: Co = 3: 2: 5 to prepare a mixed aqueous solution. Next, a solution containing citric acid in the same amount as the total number of moles of La, Ca, and Co was added to the mixed solution and stirred. Thereafter, it was dried by distillation under reduced pressure to obtain a raw material powder. This raw material powder was calcined in the atmosphere at a temperature of 200 ° C. for 2 hours, and further calcined at a temperature of 700 ° C. for 2 hours to obtain a positive electrode catalyst made of La _0.6 Ca _0.4 CoO ₃ . This is designated as Sample E2.

  Next, the lithium air secondary battery (battery E2) was produced using the sample E2. The battery E2 was produced in the same manner as the battery E1, except that the sample E2 was used instead of the sample E1 as a positive electrode catalyst.

In this example, as a comparison between the battery E1 and the battery E2, a lithium air secondary battery (battery C1) containing no positive electrode catalyst was produced.
Specifically, first, 97.4 parts by weight of activated carbon was dispersed in ethanol to prepare a dispersion. A thin-film positive electrode material was obtained by mixing 2.6 parts by weight of polytetrafluoroethylene with this dispersion. Next, a positive electrode material containing 5 mg of activated carbon was pressure-bonded to a metal mesh made of Ni and vacuum-dried to obtain a plate-shaped positive electrode. A lithium air secondary battery was produced using this positive electrode. This is designated as battery C1.
Battery C1 was produced in the same manner as Battery E1, except that a positive electrode containing no positive electrode catalyst was used.

  Next, the following charge / discharge test was performed using the three types of lithium-air secondary batteries (battery E1, battery E2, and battery C1) produced as described above, and the charge voltage and discharge voltage of each battery were examined. It was.

(Charge / discharge test)
Each battery (battery E1, battery E2, and battery C1) was discharged to a discharge lower limit voltage of 2.0 V by flowing a current of 50.5 mA per gram of carbon of the positive electrode. Next, the battery was charged to a charge upper limit voltage of 4.2 V by flowing a current of 20.2 mA per gram of carbon of the positive electrode. And the voltage and discharge capacity of each battery at this time were measured, respectively. The discharge capacity is obtained by measuring the discharge current value (mA) and multiplying the discharge current value by the time (hr) required for discharge, and dividing the value by the weight (g) of carbon in the battery. Was calculated. Similarly to the discharge capacity, the charge capacity is obtained by measuring the charge current value (mA) and multiplying the charge current value by the time (hr) required for charging, and obtaining the value obtained by weight of the carbon in the battery (g ). The results are shown in FIGS. FIG. 4 shows the relationship between the discharge capacity and battery voltage of each battery during discharge. FIG. 5 shows the relationship between the charging capacity of each battery and the battery voltage during charging. Table 1 shows the average voltage during discharging and charging for each battery.

  As is known from FIG. 4 and Table 1, the battery E1 and the battery E2 containing the positive electrode catalyst (sample E1 and sample E2) discharge at a higher voltage than the battery C1 not containing the positive electrode catalyst. I was able to. This is presumably because the overvoltage component was reduced by the positive electrode catalyst in the battery E1 and the battery E2.

  5 and Table 1, the battery E1 and the battery E2 containing the positive electrode catalyst (sample E1 and sample E2) have a voltage as low as 3.5 to 3.7 V and a relatively constant voltage. I was able to charge with. On the other hand, in the battery C1 not containing the positive electrode catalyst, the battery voltage suddenly increased after starting charging, and reached the charging upper limit voltage of 4.2 V in a short time. In addition, in the battery C1, the charge / discharge capacity was very small of 50 mAh / g or less, but in the battery E1 and the battery E3, the charge / discharge capacity was improved as compared with the sample C1.

  As described above, according to this example, by using the positive electrode catalyst for the positive electrode, it is possible to charge the lithium-air secondary battery at a low voltage and to discharge at a high voltage. .

(Example 2)
In Example 1, a lithium-air secondary battery using an oxygen permeable membrane was produced. In this example, a plurality of lithium air batteries each containing various positive electrode catalysts without using an oxygen permeable membrane were used. A secondary battery is manufactured and its characteristics are evaluated.

  As shown in FIG. 6, the lithium-air secondary battery 7 of this example includes a nonaqueous electrolytic solution as an electrolytic solution, a positive electrode 71 that oxidizes and reduces oxygen, and a negative electrode 72 that is made of metal Li. Similarly to Example 1, the positive electrode 71 is formed by pressure-bonding a positive electrode material containing a positive electrode catalyst, a carbon material, and an organic binder to a current collector.

As shown in FIG. 6, in the lithium air secondary battery 7, the positive electrode 71, the negative electrode 72, and the electrolytic solution are arranged in a battery case 74. Between the positive electrode 71 and the negative electrode 72, the separator 73 which isolate | separates these is arrange | positioned, and the non-aqueous electrolyte is impregnated with the porous separator 73. FIG. The positive electrode 71 has a contact portion 715 with air on the side opposite to the separator 73.
As shown in FIGS. 1 and 2, the battery case 74 includes a main body portion 741, a lid portion 742, and an insulating portion 743. The lid portion 742 is provided with a through hole 745 for introducing air into the battery. ing. Oxygen enters the lithium air secondary battery 7 from the through hole 745 and is supplied to the positive electrode 71. Further, the main body portion 741 and the lid portion 742 of the battery case 74 are joined together by caulking, welding, or the like via an insulating portion 743 made of an insulating material. Thus, the lithium air secondary battery 7 of this example has the same structure as the lithium air secondary battery of Example 1 except that it does not have an oxygen permeable membrane.

Next, the manufacturing method of the lithium air secondary battery of this example will be described.
First, in the same manner as in Example 1, a positive electrode catalyst (sample E1) was prepared by supporting a platinum catalyst on a CeO ₂ —ZrO ₂ solid solution.
Next, as in Example 1, 14.6 parts by weight of the positive electrode catalyst (sample E1) and 83 parts by weight of activated carbon were mixed in ethanol to prepare a mixed solution. A thin film cathode material was obtained by mixing 2.4 parts by weight of fluoroethylene. Next, a positive electrode material containing 5 mg of activated carbon was pressure-bonded to a metal mesh (current collector) made of Ni and vacuum-dried to obtain a plate-like positive electrode 71 (see FIG. 6).

Further, in the same manner as in Example 1, a nonaqueous electrolytic solution in which 1M of an electrolyte (LiPF ₆ ) was dissolved in a mixed solvent of 30 parts by weight of EC and 70 parts by weight of DEC was prepared. .
Further, in the same manner as in Example 1, the positive electrode 71 and the negative electrode 72 were arranged in the main body 61 of the battery case 6 in a form separated by a separator 73 made of a porous polyethylene sheet previously impregnated with a nonaqueous electrolytic solution. (See FIG. 6). Next, a lid 742 having a plurality of through holes 745 formed therein was disposed in the opening of the main body 741 of the battery case 74, and the lid 742 and the main body 741 were joined. Thus, the lithium air secondary battery 1 as shown in FIG. 6 was produced. This is designated as battery E3.
The battery E3 is the same battery as the battery E1 of Example 1 except that it does not have an oxygen permeable membrane.
Although not clearly shown in this example, as in Example 1, a terminal portion (not shown) that is electrically connected to the outside of the battery case 74 is provided from the positive electrode 71 and the negative electrode 72. The battery can be charged and discharged from these terminal portions.

Further, in this example, five types of lithium air secondary batteries (battery E4 to battery E8) were produced using a positive electrode catalyst different from the positive electrode catalyst (sample E3) used in the battery E3.
The battery E4 is a lithium-air secondary battery containing a positive electrode catalyst (sample E2 in Example 1) made of La _0.6 Ca _0.4 CoO _{3 in the} positive electrode.

In producing the battery E4, first, in the same manner as in Example 1, a positive electrode catalyst (sample E2) made of La _0.6 Ca _0.4 CoO ₃ was produced.
Next, an air lithium secondary battery (battery E4) was produced using this positive electrode catalyst (sample E2). A battery E4 was produced in the same manner as the battery E3 except that the sample E4 was used as a positive electrode catalyst.
Therefore, the battery E4 is a lithium-air secondary battery similar to the battery E3 except that it contains La _0.6 Ca _0.4 CoO ₃ as a positive electrode catalyst, except that it does not have an oxygen permeable membrane. These are the lithium air secondary batteries similar to the battery E2 of Example 1.

Battery E5 is a lithium-air secondary battery containing a positive electrode catalyst (sample E3) made of a composite material of CeO ₂ and Al ₂ O ₃ in the positive electrode.
In producing the battery E5, first, a positive electrode catalyst (sample E3) made of a composite material of CeO ₂ and Al ₂ O ₃ was produced.

Specifically, first, cerium nitrate and aluminum nitrate were mixed in water to prepare a mixed aqueous solution. At this time, cerium nitrate and aluminum nitrate were mixed at a mixing ratio such that the target product, CeO ₂ and Al ₂ O ₃ , was produced at a weight ratio of 89:11. Next, while stirring the mixed aqueous solution in a beaker, ammonia water was added dropwise to the mixed aqueous solution to neutralize it, thereby generating precipitates (cerium hydroxide, aluminum hydroxide). The resulting precipitate was aged by heating at 120 ° C. for 2 hours under a pressure of 2 atm. Next, by heating in the atmosphere at a temperature of 400 ° C. for 5 hours, CeO ₂ and Al ₂ O ₃ were generated, and the coexisting ammonium nitrate was evaporated and decomposed. CeO ₂ and Al ₂ O ₃ is generated here are the amorphous, in order to do this crystal grains by further calcined 5 hours at a temperature 550 ° C. in air, CeO ₂ and Al ₂ O ₃ The catalyst for positive electrodes which consists of a composite material powder was obtained. This is designated as Sample E3.
Next, an air lithium secondary battery (battery E5) was produced using this positive electrode catalyst (sample E3). A battery E5 was produced in the same manner as the battery E3 except that the sample E3 was used as a positive electrode catalyst.

Similarly to the sample E3 of the battery E5, the battery E6 is a lithium-air secondary battery containing a positive electrode catalyst (sample E4) made of a composite material of CeO ₂ and Al ₂ O ₃ in the positive electrode. The sample E4 is made of a composite material obtained by firing at a higher temperature than the sample E3, and is made of a composite material of CeO ₂ and Al ₂ O ₃ having a slightly smaller surface area than the sample E3.

In preparing the sample E4, first, in the same manner as in the sample E3, cerium nitrate and aluminum nitrate are mixed in water to prepare a mixed aqueous solution, and ammonia water is dropped into the mixed aqueous solution to neutralize the precipitate. (Cerium hydroxide, aluminum hydroxide) was produced. Further, in the same manner as the sample E3, the precipitate was aged and heated in the atmosphere at a temperature of 400 ° C. for 5 hours to generate CeO ₂ and Al ₂ O ₃ . Next, this was further calcined in the atmosphere at a temperature of 750 ° C. for 5 hours to obtain a positive electrode catalyst comprising a composite material powder of CeO ₂ and Al ₂ O ₃ . This is designated as Sample E4. That is, sample E4 is a positive electrode catalyst produced in the same manner as sample E3 except that the firing temperature was changed.
Next, an air lithium secondary battery (battery E6) was produced using this positive electrode catalyst (sample E4). The battery E6 was produced in the same manner as the battery E3 except that the sample E4 was used as the positive electrode catalyst.

The battery E7 is a lithium air secondary battery in which a positive electrode catalyst (sample E5) in which platinum is supported on a composite material of CeO ₂ and Al ₂ O ₃ (sample E3) is contained in the positive electrode.
In preparing the sample E5, first, a composite material powder of CeO ₂ and Al ₂ O ₃ similar to that of the sample E3 was prepared.
Next, dinitrodiammine platinum nitrate was dissolved in 150 ml of water in such an amount that the amount of platinum contained therein was 5 g to prepare an aqueous solution. In this aqueous solution, 95 g of the composite material powder was added and mixed, and then heated at a temperature of 500 ° C. for 3 hours, whereby 5 wt% platinum was supported on the composite material powder of CeO ₂ and Al ₂ O ₃ . A catalyst was obtained. This is designated as Sample E5. That is, the sample E5 is a positive electrode catalyst in which platinum is supported on the same composite material as the sample E3.
Next, an air lithium secondary battery (battery E7) was produced using this positive electrode catalyst (sample E5). A battery E7 was produced in the same manner as the battery E3 except that the sample E5 was used as a positive electrode catalyst.

The battery E8 is a lithium air secondary battery containing a positive electrode catalyst made of MnO _{2 in the} positive electrode.
In preparing the battery E8, first, a positive electrode catalyst (sample E6) made of MnO ₂ was prepared. A commercially available product was used as MnO ₂ .
Next, an air lithium secondary battery (battery E8) was produced using this positive electrode catalyst (sample E6). A battery E8 was produced in the same manner as the battery E3 except that the sample E6 was used as a positive electrode catalyst.

Moreover, in this example, the lithium air secondary battery (battery C2) which does not contain the catalyst for positive electrodes was produced for the comparison of the said battery E3-battery E8.
Specifically, first, as in the case of the battery C1 of Example 1, 97.4 parts by weight of activated carbon was dispersed in ethanol to prepare a dispersion, and polytetrafluoroethylene 2.6 was added to the dispersion. A thin film positive electrode material was obtained by mixing parts by weight. Next, a positive electrode material containing 5 mg of activated carbon was pressure-bonded to a metal mesh made of Ni and vacuum-dried to obtain a plate-shaped positive electrode. Using this positive electrode, a lithium-air secondary battery was fabricated in the same manner as the battery E3. This is referred to as a battery C2.
The battery C2 is a lithium-air secondary battery similar to the battery E3 except that the positive electrode does not contain a positive electrode catalyst, and the battery C2 is the same as that of Example 1 except that it does not have an oxygen permeable membrane. It is a lithium air secondary battery similar to the battery C1.

Next, using the seven types of lithium-air secondary batteries (battery E3 to battery E8 and battery C2) produced as described above, Example 1 was performed under room temperature conditions (temperature 30 ° C. or temperature 25 ° C.). A similar charge / discharge test was conducted to examine the charge voltage and discharge voltage of each battery.
Table 2 shows the results of the charge / discharge test conducted at a temperature of 30 ° C. Moreover, the relationship between the discharge voltage of each battery at the time of the discharge at this time and a battery voltage is shown in FIG. Moreover, the relationship between the charging voltage of each battery at the time of charge and a battery voltage is shown in FIG.
Table 3 shows the results of a charge / discharge test conducted at a temperature of 25 ° C.

  As is known from FIG. 7 and Table 2, when the charge / discharge test was performed under the condition of a temperature of 30 ° C., the batteries E3 to E8 containing the positive electrode catalysts (samples E1 to E6) were the positive electrode catalysts. It was possible to discharge at a higher voltage compared to the battery C2 not containing. This is presumably because, in the batteries E3 to E8, as in Example 1, the overvoltage component was reduced by the positive electrode catalyst.

  Further, as is known from FIG. 8 and Table 2, the batteries E3 to E8 containing the positive electrode catalysts (samples E1 to E6) have a low voltage of 3.5 to 3.8 V and a relatively constant voltage. I was able to charge with. On the other hand, in the battery C2 that does not contain the positive electrode catalyst, the battery voltage suddenly rises after the start of charging, reaches the charging upper limit voltage of 4.2V in a short time, and further exceeds 4.5V. It reached. Further, in the battery C2, the charge / discharge capacity showed a very small value of 50 mAh / g or less, but in the batteries E3 to E8, the charge / discharge capacity was improved as compared with the sample C1.

Moreover, when the charge / discharge test was conducted under the condition of a temperature of 25 ° C., almost the same result was obtained.
That is, as is known from Table 3, the batteries E3 to E8 were able to discharge at a higher voltage than the battery C2.
Further, the batteries E3 to E8 could be charged with a relatively low voltage of 4 to 4.3 V and a relatively constant voltage even under the condition of a temperature of 25 ° C. On the other hand, the battery voltage of battery C2 suddenly increased after charging was started. The battery voltage reached the discharge upper limit voltage of 4.2 V in a short time, and further exceeded 4.5 V.

  As described above, in the lithium air secondary battery (battery E3 to battery E8) of this example, a voltage lower than the decomposition potential (about 4.5V) of the nonaqueous electrolytic solution of 3.5V to 4.3V at room temperature. Charging can be performed. Therefore, in a lithium air secondary battery using a non-aqueous electrolyte, charging can be performed stably. Moreover, the lithium air secondary battery (battery E3-Taji E8) of this example can discharge with a comparatively high voltage.

1 is a perspective view showing an entire lithium air secondary battery according to Example 1. FIG. 1 is a cross-sectional view of a lithium air secondary battery according to Example 1. FIG. 1 is a cross-sectional view of a positive electrode of a lithium air secondary battery according to Example 1. FIG. The diagram which shows the relationship between the discharge capacity of 3 types of lithium air secondary batteries (battery E1, battery E2, and battery C1) at the time of discharge and battery voltage concerning Example 1. FIG. The diagram which shows the relationship between the charge capacity of three types of lithium air secondary batteries (battery E1, battery E2, and battery C1) at the time of charge and battery voltage concerning Example 1. FIG. Sectional drawing of the lithium air secondary battery concerning Example 2. FIG. The diagram which shows the relationship between the discharge capacity of 7 types of lithium air secondary batteries (battery E3-battery E8, and battery C2) at the time of discharge and battery voltage concerning Example 2. FIG. The diagram which shows the relationship between the charging capacity of 7 types of lithium air secondary batteries (battery E3-battery E8, and battery C2) at the time of charge and battery voltage concerning Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium air secondary battery 2 Positive electrode 21 Current collector 22 Carbon material 23 Cathode catalyst
3 Negative electrode 4 Separator

Claims (14)

A positive electrode catalyst used for a positive electrode of a lithium-air secondary battery having a non-aqueous electrolyte as an electrolyte and a negative electrode made of metal Li,
The positive electrode catalyst contains a metal oxide having an oxygen absorption / release capability,
The positive electrode catalyst characterized by containing at least CeO ₂ as the metal oxide. In claim 1, the catalyst for the positive electrode, the catalyst for the positive electrode, characterized in that it contains a CeO ₂ solid solution. 3. The positive electrode catalyst according to claim 2, wherein the positive electrode catalyst contains a solid solution of CeO ₂ and ZrO ₂ . The positive electrode catalyst according to claim 1, wherein the positive electrode catalyst contains a composite material of CeO ₂ and Al ₂ O ₃ .   5. The composite material according to claim 4, wherein an alkali is added to an aqueous solution obtained by dissolving a cerium salt and an aluminum salt in water to form a precipitate containing cerium hydroxide and aluminum hydroxide, and the precipitate is fired. The catalyst for positive electrodes characterized by these. A positive electrode catalyst used for a positive electrode of a lithium-air secondary battery having a non-aqueous electrolyte as an electrolyte and a negative electrode made of metal Li,
The positive electrode catalyst contains a metal oxide having an oxygen absorption / release capability,
A positive electrode catalyst comprising at least MnO ₂ as the metal oxide. A positive electrode catalyst used for a positive electrode of a lithium-air secondary battery having a non-aqueous electrolyte as an electrolyte and a negative electrode made of metal Li,
The positive electrode catalyst contains a metal oxide having an oxygen absorption / release capability,
The metal oxide contains a perovskite complex oxide represented by ABO ₃ , and the perovskite complex oxide contains at least two selected from La, Sr, and Ca as an A site element, A positive electrode catalyst comprising at least one selected from Mn, Fe, Cr, and Co as a B site element.   8. The positive electrode catalyst according to claim 1, wherein a noble metal is supported on the metal oxide.   9. The positive electrode catalyst according to claim 1, wherein the positive electrode catalyst is used for the lithium-air secondary battery that is charged at an average voltage of 3.5 V to 4.3 V. 10. In a lithium air secondary battery having a non-aqueous electrolyte as an electrolyte and a negative electrode made of metal Li,
The lithium air secondary battery comprises the positive electrode catalyst according to any one of claims 1 to 9 in a positive electrode.   11. The lithium air secondary battery according to claim 10, wherein the positive electrode is formed by pressure-bonding a positive electrode material containing the positive electrode catalyst, a carbon material, and an organic binder to a current collector.   In Claim 11, the said catalyst for positive electrodes occupies 0.01-50 mass% in the total amount of the said catalyst for positive electrodes, the said carbon material, and the said organic binder in the said positive electrode. Next battery.   In any one of Claims 10-12, the said lithium air secondary battery has the separator which isolate | separates these between the said positive electrode and the said negative electrode, and the said non-aqueous electrolyte, The said positive electrode is A lithium-air secondary battery having a contact portion with air on the side opposite to the separator.   14. The lithium air secondary battery according to claim 13, wherein the metal oxide contained in the positive electrode catalyst absorbs and releases oxygen by an oxidation-reduction reaction at the contact portion.

Images